21312215 has 8 divisors (see below), whose sum is σ = 25747200. Its totient is φ = 16934752.

The previous prime is 21312173. The next prime is 21312223. The reversal of 21312215 is 51221312.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21312215 - 2⁸ = 21311959 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21312193 and 21312202.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13559 + ... + 15048.

It is an arithmetic number, because the mean of its divisors is an integer number (3218400).

Almost surely, 2^21312215 is an apocalyptic number.

21312215 is a deficient number, since it is larger than the sum of its proper divisors (4434985).

21312215 is a wasteful number, since it uses less digits than its factorization.

21312215 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28761.

The product of its digits is 120, while the sum is 17.

The square root of 21312215 is about 4616.5154608211. The cubic root of 21312215 is about 277.2529630599.

Adding to 21312215 its reverse (51221312), we get a palindrome (72533527).

The spelling of 21312215 in words is "twenty-one million, three hundred twelve thousand, two hundred fifteen".